Today was the day of judgement, the measure of my building
prowness- no, not the first flight, but the weight and
balance. My plane weighs 1091 lbs, weighed as it should
be- no usable fuel, full oil and coolant. I for one would
go with the aluminum housings if they cost me up to $1500
more than the cast iron ones. If they saved 70 lbs total,
that would be around $21 for each pound saved, to get my
plane down to a more svelte 1021 lbs. I'm sure I could
probably get another 15 lbs off if I did some weight
reduction on my Shertz beam front mount, along with other
things. I also went a bit heavy on my engine mount- 1"
dia x .049 thick tubes on some of the mount. I at least
have confidence that my mount should hold up. The CGs all
work out OK- design range is between 6 8.7 -77.7 inches
aft of datum. Here is how it works out:


Vans states that most RV-4s come in around 950 lbs. Gross recommended is
1500 lbs.

Mine:
Empty 66.2, wt.1021 lbs with 180 lb pilot, but no
fuel-68.51, just a bit out of CG by .2 inches, total wt.
1271 with 180 lb pilot and full fuel 68.8, total wt. 1465-
with 35 lbs baggage- cg-70.38 total 1500

If I want to take a passenger with full fuel and baggage,
they'd better not weigh a thing, or I'll be flying over
gross recommended weight.

Brian Trubee

Jeff's motor plate will help as it in effect eliminates the 9 pound weight
of
the Scheretz beam. It weighs about the same as Tracy's plate but
the motor mounts are built in. Not helpful for Brian as he is too far
gone for a new motor mount.

One inch .049" tubing weighs about .0462 pounds per inch. Four pieces
30 inches long therefore weighs 5.5 pounds. 3/4 OD .049 4130 tubing
weighs .0346 pounds per inch so if you replaced just the top two tubes
with 3/4 you would save 2 pounds. Careful design is important with
no tubes in bending.

I think 10 pounds can be gotten out of Tracy's gear box with out too much
trouble. See the attached PSRU parts weights.

Aluminum end housings are $1500 each. I am not sure about the TBO however.

If you are 100 pounds over gross your climb rate assuming the
same power will be down 1500/1600 or .9375%. Top speed will hardly
be affected. If the climb rate is given as 1500 FPM with a 150 HP
O-360 than a P-port rotary would be about 2500 FPM. I suspect a
few pounds would be saved in the intake manifold with a p-port
slide throttle setup.

--------------------------------------------------
Correction on the tube savings. 30 inch 1 inch OD tubes
weigh 1.375 pounds each for a total of 5.5 pounds.
So you would only save about a pound and not two pounds.

If a tube is in tension or real short use 3/4.

Also 2500 FPM P-port estimate is a bit high. More like 2000 FPM.

Paul Lamar

I was reading a reply to my posting "weighty matters" and
saw that I had mis stated the weight of the airplane.  It
is not 1021 lbs, its 1091 lbs, EMPTY.  That's 140 lbs over
what they generally come in at.  Not something that would
sell a rotary engine conversion.  Obviousy, this is much
more than I wanted to end up with, but I'll fly it and then
start a Jenny Craig program for this airplane.


Brian Trubee

Brian, What does the aluminum cowl weigh and how does that compare to the
stock cowl? How thick is it?

Mike Wills, What does your RV4 weigh?

Paul Lamar


Paul,

My RV was 1027 empty. I've been pretty upset about it until I heard Brian's
weight (sorry Brian). :-)

My cowl has gained weight over the years as I cut holes and then patched
them trying to come up with an oil cooler install that would have a chance,
and the exhaust clearance blister I had to add.

I have 2 Odyssey batteries, 14 pounds each, in the baggage compartment for
CG reasons. If I lost a battery and could shed some FWF weight so I could
relocate the remaining battery where it actually belongs I could save close
to 20 pounds ( 0AWG cable is heavy!).

My single radiator probably carries a bit more water weight than the typical
setup with AC cores.

My oil cooler plumbing is all steel braided and is pretty long - probably a
couple of pounds.

My exhaust header is a true 2 - 1 with equal length primaries 32" long 1
3/4" x .065" 321 stainless. Its heavy!

My seat cushions are all Temperfoam - also very heavy.

The list goes on and on. A few pounds here and there and I'm sure I could
get 50 pounds off of it, but would take a lot of work. I don't think its
possible to get down to the 930 pounds Tracy claims without a do-over.

Currently my best rate of climb at SDM (525 MSL) is initially about 1700fpm
and that's with the engine still not making full power (not sure if the
limitation is engine or prop; I cant get 6000 RPM straight and level with a
2.17 reduction ratio). So I'm OK with the weight now with the thought that
somewhere in the future there's still more performance trying to get out.
I'd recommend Brian not sweat it too much. As long as the engine makes
decent power and the prop is close the airplane will perform fine.

Mike Wills